1. Field of the Invention
The invention is concerned, generally, with a device for coating particles, particularly drugs in the form of particles, such as tablets and similar items. The device has a support, a drum resting in it, in such a way that it may rotate around a pivot or drum axis, said drum having a wall with an--at least, partially--perforated part, and with a gas transmission shoe that, in operation, is held by the support and lies against the aforementioned wall part, so as to make it possible for a gas to flow through it.
As to the concept of "drug particles", we want to state that, by it, solid pharmaceuticals (drugs) or pharmaceuticals that, at least, have a solid covering, i.e. so-called solid forms of administering medicines, such as tablets as well as pills and capsules, are to be understood.
2. Description of the Prior Art
From the U.S. Pat. No. 3,601,086, a device for the coating of tablets is known that comprises a support, a drum that may be rotated around a horizontal axis, and a driving mechanism for rotating the drum. The front side of the drum has been provided with a central opening.
On the opposite side, the drum is closed, connected with the driving mechanism by means of a flange-connected trunnion, and rests in the driving mechanism. The drum has a cylindrical perforated jacket part. In the support, within the region of the one lower quadrant of the drum, a suction shoe is held, in such a way that it may rotate, said suction shoe being capable of being pressed by a compressed-air cylinder by way of a lever system against the perforated jacket part of the drum. The suction shoe is connected with a suction fan, in such a way that, when the device is in operation, air can be sucked out of the interior of the drum through the perforated part of the jacket, the suction shoe, and the duct. The tablets to be coated are fed into the drum through the opening provided in it on the front side and will be removed again from the drum through that same opening after the coating has been applied.
In the devices developed in accordance with U.S. Pat. No. 3,601,086 and known in the market place, a casing enclosing the drum on all sides has been provided. The air is introduced into the casing on top and then sucked into the drum, while a large part of it flows through the perforation in the jacket of the drum. Further, the casing of the device known in the market place has been provided with a door in the region of the opening that is present on one opening in the drum on one of its front sides.
When the drum comes to a standstill, the tablets collect in its bottom part. Therefore, the drum must be raised for removing the tablets, in some way, up to the frontal opening of the drum. Thus, the removal of the tablets is made more difficult. It is also possible that the coatings applied to the tablets may be damaged when the tablets are lifted out of the drum.
The devices, and in particular also the drums, have to be cleaned from time to time,--at least, when the processed product is changed. For proper cleaning, the drums should be scrubbed with a brush, inside and outside. But, in the devices in accordance with the U.S. Pat. No. 3,601,086, the interior of the drum is accessible from one side only, which complicates the cleaning of the drum considerably. That is particularly true in the case of relatively large drums, the measurements of which, taken in the direction of the pivot, may amount to as much as approximately 5 m.
Moreover, the suction shoe can be moved only a relatively short distance away from the drum, which also hampers the cleaning of the outside of the drum and the suction shoe.
Another disadvantage of the devices in accordance with the U.S. Pat. No. 3,601,086 is to be found in the fact that the driving mechanism which is located by the side of the drum and is used to support the drum, also complicates the accessibility of the parts to be cleaned and, moreover, requires a relatively large amount of space, viz. according to the description in the patent, approximately as much space as the drum itself.
When the aforementioned door in the casing is opened for an inspection of the contents of the drum, while a coating is applied to the tablets, frequently a surge of air containing a large part of sprayed coating material passes from the drum into the environment, and that is also a disadvantage.
When a device is used, relatively small and relatively large amounts of tablets are fed into the drum, at various times. In addition, the tablets may have different mobilities, depending on their size, form, and other properties. For those reasons, the coating of the tablets, which is the result of rotation, may have different dimensions, from time to time.
The suction opening of the suction shoe is not described in any detail in the U.S. Pat. No. 3,601,086. In devices that have been developed in accordance with that patent, and which are known in the market place, the suction opening is circumscribed by fixed bounds. When, during the rotation of the drum, a tablet coating is created that, when measured along the circumference of the drum, has relatively large dimensions, air is passed through a relatively small part of that tablet charge only, and the effectiveness of the coating process will be reduced thereby. Conversely, when the tablet coating along the circumference of the drum has relatively small dimensions only and does not extend over the entire opening of the suction shoe, a large part of the air will be sucked through alongside the tablet coating which, as a matter of course, reduces the degree of effectiveness of the device a considerable extent.
Moreover, the device known from the U.S. Pat. No. 3,601,086 provides only for an operation in which the air is sucked out of the drum into the suction shoe. But, it has become evident that that modus operandi has only unsatisfactory results, in the case of certain applications.
From the U.S. Pat. No. 3,834,347, a device for the coating of tablets is known that also presents a drum that may be rotated around a horizontal axis and has a cylindrical mantle. The latter is largely free of holes, and is perforated only at four relatively narrow bands that run parallel to the axis of the drum and are distributed over the circumference of the drum. Each perforated band of the mantle is sealed off from the environment by means of a hood mounted on the outside of the drum. Said hoods form the boundaries of four suction ducts that rotate with the drum during the operation of the device, and that are connected, in a specified rotational position of the drum, with a stationary suction line by way of an indraft coupling mounted on one face of the drum. The mantle has been provided, between two indraft ducts, with an opening for the removal of the tablets that has been provided with a cover which projects toward the outside of the mantle of the drum.
It is true that, in the device in accordance with U.S. Pat. No. 3,834,347, the drum can be emptied with relative ease, after a coating has been applied to the tablets. But, in this device, it is difficult to clean the suction ducts and the indraft couplings, and it is even practically impossible to check up on their being clean. That is a grave disadvantage in the manufacture of pharmaceutical products where high demands are made on purity. According to German Pat. No. 1,225,035, a device is known for the candying of confectionery that has a support and a drum that rotates around a horizontal axis. The drum has been provided with two barrel rings each of which rests on two rubberized friction rollers mounted in the base of the housing. Accordingly, the drum does not have any bearing proper, but is supported solely by the friction rollers. The motor and the gearing for driving the device are housed in the base below the drum. Both faces of the drum have been provided with one opening each. The drum also comprises, within the area of the mantle, another opening, which may be closed by means of a flap, for the removal of the processed material.
In the device known from the German Pat. No. 1,225,035, the mantle of the drum does not present any perforations, and there are no other means for sucking the air through a tablet bed that is present in the drum during operation. But, as a matter of fact, there would be sufficient room between the barrel rings of the drum, the friction rollers, and their shafts which are mounted on top of the base, to house a suction shoe.